Effects of pH and temperature on coupling nitritation and anammox in biofilters treating dairy wastewater

► Furnace slag and marble chips raised pH to enhance nitritation–anammox in biofilters. ► Ammonium oxidizing and anammox bacteria accounted for 69–74% of bacterial population. ► Ammonium removal rate was significantly higher at pH 8.1 than pH 7.6. ► Free ammonia concentration should be controlled to avoid inhibition to anammox. ► Temperature effects were superior to pH effects on simultaneous nitritation–anammox. Simultaneous nitritation and anammox is a novel process for nitrogen removal from wastewater. This study operated two innovative biofilters to examine the effects of pH and temperature on the nitritation–anammox process. Marble chips were packed in the biofilters to buffer pH and supplement alkalinity. Electric arc furnace slag was added to marble chips in one biofilter to further increase pH to favor nitritation over nitratation. After a 5-month startup period, the biofilters were batch loaded with dairy wastewater and drained weekly over seven months. Fluorescence in situ hybridization analysis found that aerobic ammonium oxidizing and anammox bacteria accounted for 69–74% of the bacterial populations in the biofilters, which were substantially higher than those reported earlier for constructed wetlands and biofilters. Ammonium removal rate was significantly higher in the biofilter at pH 8.1 (7.8±1.2gN/m3d) than that in the other biofilter at pH 7.6 (6.4±1.3gN/m3d). Free ammonia concentration should be controlled along with pH to avoid toxicity to anammox bacteria. There was no significant correlation of nitrogen removal with the seasonal variation of temperature. Temperature effects were further examined for another five months by heating one of the biofilters. Ammonium removal rate was greater (23.7±3.3gN/m3d) in the heated biofilter at 28.8±1.1°C than that in the unheated biofilter (7.6±2.4gN/m3d) where temperature fluctuated at 21.2±3.2°C. The effects of constant temperature were superior to pH effects on nitritation–anammox. The nitritation–anammox process is more sensitive to temperature than nitritation and anammox individually. This study demonstrated that waste products (marble chips and furnace slag) can be used in biofilters to effectively raise pH and enhance nitritation–anammox for nitrogen removal from dairy wastewater.